A100-year flood is the flooding elevation that has a one percent chance of happening each year. why is the name misleading

One percent annual chance of flooding does not mean it will happen with absolute certainty once every 100 years. Just that the expected value of a flood in 100 years is one.

As an example, heads has a 50% chance of happening every coin flip. With 2 coin flips, the expected value is one. However, it would be a misnomer to call "heads" a 2-flip outcome.

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.